In recent power conversion apparatuses for saved energy and new energy, many inverters and converters are used. In order to realize a low carbon society, considerable spread of them becomes essential.
As a power semiconductor element for a power conversion apparatus, an insulated gate bipolar transistors (hereinafter referred to as “IGBT”) has been widely used. The IGBT has the excellent property of being low in an on-state voltage and high in switching speed, that is, being low in both of a conduction loss and a switching loss, as an element for a power conversion apparatus. Moreover, the IGBT also has easy controllability by an insulating gate, so that it has been currently used widely in articles including low power equipment, such as an air-conditioner and a microwave oven, to high power equipment, such as an inverter for a railway and an iron factory.
According to the spread of the power conversion apparatuses, further improvement in performance of the IGBT is required. However, there is trade-off relation between the conduction loss and the switching loss, so that considerable improvement in the performance of the IGBT is difficult.
Thus, as technologies that reduce both of the conduction loss and switching loss of the IGBT, there have been known a structure in which an insulating gate electrode is divided into a plurality of sections that are controlled independently (refer to Patent Literature 1, 2, and 3, for example), and a structure in which an insulating gate electrode is provided on a back surface (collector side) (refer to Patent Literature 4, 5, 6, 7, and 8, for example).
The structure, in which the gate electrode is divided into the plurality of sections, and the structure, in which the insulating gate electrode is provided on the back surface, can respectively take two modes, that includes a mode low in an on-voltage, viz., a mode large in a turn-off loss, and a mode high in the on-voltage, viz., a mode small in the turn-off loss, by a second gate electrode on a front surface and the gate electrode on the back surface. At the time of conduction and turn-off, the two states are switched, thereby making it possible to reduce both of the conduction loss and switching loss